This invention is directed to a novel method and apparatus for accurately measuring volume of gas flowing as a result of differential pressure. More particularly, the present invention is directed to a method and apparatus for accurately measuring volume of compressed natural gas (CNG) flowing into gas cylinders of a motorized vehicle, such as a truck, van, car and the like. Such gas volume is preferably referenced to standard temperature and pressure.
It is currently desirable to use CNG as an alternate but not simultaneous fuel in motorized vehicles using gasoline or diesel fuel. It is also desirable that the volume of CNG that is transferred into the CNG gas cylinders of such a motorized vehicle be known with a relatively acceptable degree of accuracy. It is further desirable that the method of filling such vehicle CNG gas cylinders be relatively quick.
Commercially available conversion kits for adapting vehicle engines to CNG operation are well known. However, commercially available equipment for recording volume of CNG transferred into such vehicles is either inaccurate, unreliable or both. For example, commercially available turbine meters have been observed to be high maintenance items; and a commercially available vibrating U-shaped sensor used for measuring mass flow rates was observed to develop inaccuracies as CNG specific gravity units (SGU's) varied.